Proper 4R Practices Can Lessen Ammonia Toxicity in Roots

Alan Blaylock, Ph.D.

Banding nutrients near, below or even in the seed row is a common practice in western dryland cropping systems. However, these placements are a source of risk in stand establishment and seedling root damage. Recent studies at Washington State University by Drs. Isaac Madsen and William Pan have evaluated these risks using a novel and inexpensive imaging technique to assess the rate, source, and placement options when banding nitrogen fertilizers near the seed at planting.

Survival analysis was conducted on canola roots growing into bands of urea, ammonium sulfate (AS) and urea-ammonium nitrate (UAN) and LD50s – lethal dose that results in 50 percent reduction in population – were estimated. Wheat roots were visually assessed for damage when exposed to bands of urea and diammonium phosphate (DAP). In all instances, urea was shown to be the most toxic source of nitrogen. Care should be taken when banding nitrogen fertilizers to account for source and rate in order to prevent root damage. Results of this study were presented at the 2019 Western Nutrient Management Conference. Download the paper here (Assessment of Relative Potencies of Nitrogen Sources on Seedling Root Systems).